The invention relates in general to heat generating structures, and more particularly to a relatively slow burning, gasless heating element that may be utilized for various purposes such as a delay element or fuse that ignites an explosive device or material.
It is known that a heat generating structure composed of two dissimilar materials such as metals may be used as an ignitable delay element or fuse. The delay element may be used in varied applications to safely initiate the timed ignition or detonation of an explosive device or material. These heat generating structures can come in many different physical forms. For example, known ignitable delay elements comprised of compressed powder mixtures can be unreliable and exhibit unacceptable delay timing (e.g., timing differences between similarly manufactured elements) or initiation-sensitive variations. These problems are due, for example, to particle size distribution inconsistencies, inadequate mixing, free volume and pressure. In addition, such an undesirable performance variation tends to become more pronounced as the propagation rate of the delay element is reduced. Further, powder-type delay mixtures produce at least some gas, the production of which requires the incorporation of hardware structures that prevent the premature and undesired heating and possible ignition of the “target” (the substance, often an explosive, which ignites when the delay has run its course or completed its propagation) by such hot gas production. Also, the production of such gases by these powder mixtures is oftentimes influenced by pressure and packing variations.
Other known heat generating structures that can be used as delay elements include that which is commercially available under the brand name Pyrofuze® provided by the Sigmund Cohn Corporation of Mount Vernon, N.Y. This device comes in wire or ribbon form and comprises two metallic elements in intimate contact with one another: an inner core of aluminum surrounded by an outer jacket of palladium. When the two metallic elements are brought to the initiating temperature by a sufficient amount of heat, the metals react by alloying rapidly resulting in instant deflagration without support of oxygen. Once the alloying reaction is started, the reaction will not stop until alloying is completed. One drawback with the Pyrofuze® delay element is that it typically burns at a relatively rapid rate.
Another commercially available heat generating structure that can be used as a delay element or fuse is provided under the brand name NanoFoil® by Reactive NanoTechnologies, Inc. of Hunt Valley, Md. The NanoFoil® device is a multilayer foil comprised of thousands of alternating nanoscale thin layers of aluminum and nickel. When initiated by an electrical, thermal, mechanical or optical source, the metals will mix or alloy and react to release heat energy. However, when used as a delay element or fuse, the NanoFoil® multilayer foil tends to have a burn rate that is relatively fast, and the burn rate is not easily variable. The NanoFoil® multilayer foil is also relatively expensive.
What is needed is a relatively slow burning, gasless, heat generating structure composed of two or more dissimilar materials, such as metals, distributed in a non-uniform three-dimensional manner along its propagation or burn path, where the structure when ignited exhibits an exothermic alloying reaction between the materials and can function as a delay element or fuse in providing for reliable propagation and, thus, accurate ignition of an explosive device.